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We construct a reliable actively Q-switched Nd:YVO4 laser to comparatively investigate the output performance of the second harmonic generation between the extracavity and intracavity configurations under a similar operated condition. It is experimentally found that the peak power at 532 nm obtained with the extracavity second harmonic generation is remarkably higher than that obtained with the intracavity configuration, even though the higher output power and larger pulse energy can be acquired with the intracavity second harmonic generation. We further perform the extracavity fourth harmonic generation to verify that the extracavity second harmonic generation is more advantageous in generating deep ultraviolet laser at 266 nm than the intracavity one, where the conversion efficiencies from 532 to 266 nm for each case are 37.1% and 7.2%, respectively. Moreover, under an incident pump power of 26 W at 808 nm and a pulse repetition rate of 40 kHz, the output power at 266 nm as high as 1.67 W is effectually generated with the combination of the extracavity second and fourth harmonic generations, corresponding to the conversion efficiency from 808 to 266 nm up to 6.4%.

A LED-array-pumped Nd:YAG laser with optical conversion efficiency up to 20.2% is demonstrated by direct side-pumping without a coupling lens. The 810-nm LED array with a full-width-half-maximum of 30 nm and an area fill factor of 50% is designed to attain high spectral absorption efficiency with a pump density of 151.8 W/cmsup2/sup. Furthermore, higher than 45% overall coupling efficiency is achieved by placing the LED array as close as possible to the side of the gain medium for overcoming the large pumped divergence. More importantly, by using the efficient pump scheme, the demonstration of a passively Q-switched LED-pumped laser is successfully realized with a pulsed energy of 1.42 mJ.

A synchronously dual self-mode-locked (SML) operation at 946 and 1064 nm is experimentally accomplished by using a compact coupling scheme to obtain the optical beating frequency up to 35.2 THz. The SML emissions at 946 and 1064 nm are established by a monolithic Nd:YAG cavity and a Nd:YVOsub4/subcrystal in a flat-flat cavity, respectively. Two gain media are butt adjoined to be longitudinally pumped by a single laser diode. The monolithic Nd:YAG crystal is used not only as the 946 nm laser cavity, but also as the output coupler of the Nd:YVOsub4/sub1064 nm laser. More importantly, the output surface of the monolithic Nd:YAG laser is coated to generate the optical feedback for the synchronization of the dual SML operation. At a pump power of 10.7 W, the output powers at 1064 and 946 nm can simultaneously reach 1.5 W by controlling the focal position of the pump waist.

An efficient LED pumping module is explored for the demonstration of energy scaling of passively Q-switched output to millijoule high-pulse-energy level. For the free-running operation at fundamental wavelength, the highest optical conversion efficiency of 23.7% is reached. By using a Cr4+:YAG crystal as the saturable absorber, the passively Q-switched output energy is up to 14.5 mJ in a compact setup. The laser resonator is further optimized to shorten the output pulse width and to obtain better mode quality. The pulse width of the Q-switched emission is as short as 25 ns, and the peak power is up to 0.7 MW. With such a highly efficient configuration, the extracavity second-harmonic generation at 532 nm can be achieved with 4.5 mJ pulse energy.

An orthogonally polarized self-mode-locked Nd:YAG laser is demonstrated in a short linear cavity. Under an incident pump power of 8.2 W, the average output power can be measured to be 3.8 W. The beat frequency Δfc between two orthogonally polarized mode-locked components is observed and increases linearly with an increase in the incident pump power. The origin of the beat frequency is utterly confirmed to be caused by the thermal-stress-induced birefringence in the Nd:YAG crystal and is theoretically simulated. The present result provides a promising method to achieve orthogonally polarized mode-locked lasers with tunable beat frequency.

The self-mode-locked (SML) operation at 946 nm can be achieved with a monolithic Nd:YAG crystal when the pump power is above the threshold of the multiple-longitudinal-mode generation. The SML output is further found to include two orthogonal polarization components with a beat frequency coming from the birefringence effect in the laser crystal. The beat frequency can be widely adjusted in the range of 5−220 MHz by controlling the cooling temperature. The present experiment also confirms the theoretical prediction that the two-mode operation generally exhibits the chaotic dynamics when the frequency difference is sufficiently close to the relaxation frequency.

A dual-wavelength self-mode-locked monolithic Nd:YAG laser at 1061 and 1064 nm is realized at cryogenic temperatures. At an incident pump power of 5.5 W, the total output power can reach 2.5 W and the mode-locked pulse width is 29 ps at a pulse repetition rate of 7.75 GHz. The synchronization of the dual-wavelength emissions leads to a beat frequency of 670 GHz in the individual mode-locked pulse. It is further discovered that the laser output consists of two orthogonally polarized components with a central frequency difference of 127 MHz. The central frequency difference between two orthogonal polarizations mainly arises from the external mechanical stress introduced by the copper holder for the laser crystal.

We thoroughly develop compact high-peak-power Nd:YVO4/Cr4+:YAG passively Q-switched lasers (PQS) as the seed source of the fiber amplifier. We exploit a nearly hemispherical cavity to reach the second threshold criterion and systematically consider the thermal lensing effect and the mode-size matching in the overall optimization. Employing a Cr4+:YAG absorber with 70% initial transmission, we obtain a 50-kHz seed pulse train with the pulse duration of 4.8 ns and the pulse energy of 22 μJ at a pump power of 5.4 W. Injecting this seed laser into a polarization maintained Yb-doped fiber, the pulse energy and peak power at a pump power of 16 W are enhanced up to 178 μJ and 37 kW, respectively. We also use an absorber with 40% initial transmission to generate a 25 kHz pulse train with the pulse duration of 1.6 ns and the pulse energy of 36 μJ at a pump power of 5.4 W. With this seed laser, we find that the surface damage of the fiber limits the maximum pulse energy and peak power to be 192 μJ and 120 kW, respectively.

The criterion for achieving power scaling of the cryogenically cooled monolithic 946 nm laser is investigated by varying crystal length. Theoretical analysis of the mode-to-pump size matching indicates that the optimal power can be obtained with a crystal length of 8 mm. Furthermore, the pump–wavelength dependence of the output power can be less sensitive when a longer crystal was employed. We demonstrate 946 nm monolithic lasers with various crystal lengths to verify the theoretical analysis. The highest output power (30.2 W) is obtained by using an 8 mm Nd:YAG crystal at 130 K. Moreover, the output power reduction ratio is found to be smaller than 15% with the pump wavelength fluctuating between ±1 nm.

A dual-wavelength laser at four-level and quasi-three-level transitions is demonstrated in a linear resonator. The compactly combined Nd:YAG and Nd:YVO 4 crystals successfully improve the efficiency limitation for the dilemma between reabsorption loss and absorption reduction.

We employ a plane wave to perform interference with the circularly geometric beam from off-axis pumped solid-state lasers. The good agreement between the experimental and calculated interference patterns indicates vortex structures of circularly geometric beams.

The thermally insensitive feature of convex-concave cavity is confirmed that can achieve power scaling in a wide-range cavity length. The influence of cavity length on the self-mode-locking behavior in this cavity is further explored.

A Nd:YLF laser is cryogenically cooled for the demonstration of orthogonally polarized dual-wavelength emissions at 1047 nm and 1053 nm. The approach of passively Q-switching with less thermal effect is also experimentally investigated.

A cryogenically monolithic Nd:YVO4 self-Raman laser is experimentally explored and theoretically analyzed. The variation of the stimulated Raman scattering (SRS) threshold on the temperature is found to be nonlinear because the reduction of thermal lensing enlarges the cavity mode size. In spite of the nonlinear variation of the SRS threshold on the temperature, the overall SRS output power can be efficiently increased from 0.78 to 1.36 W for temperature decreasing from 285 to 80 K at an absorbed power of 17.2 W. More interestingly, the single-longitudinal-mode operation is experimentally achieved when temperature is lower than 125 K.

An intrinsic silicon wafer is exploited as an output-coupler to develop a high-peak-power optically-pumped AlGaInAs laser at 1.52 mm. The gain chip is sandwiched between diamond heat-spreaders and Si-wafer to form a compactly stack cavity.

A Q-switched mode-locked Nd:YAG laser is utilized to explore air breakdown threshold in a statistical approach to be 0.64 TW/cm2. The temporal dynamics of induced plasma shows a sub-nanosecond delay to the incident Q-switched pulse.

An optimal temperature of 130 K is observed for the cryogenic 946-nm monolithic Nd:YAG laser. The pump criterion is discussed and the output power is up to 24 W with conversion efficiency of 71%.

A Nd:YLF laser at cryogenic temperature is demonstrated for the first time with orthogonally polarized simultaneous emission at 1047 nm and 1053 nm. By exploring the temperature dependence of the fluorescence and the absorption spectra from the Nd:YLF crystal, the feasibility of simultaneous emission at low temperature is achieved. Due to the local heating from the pump absorption, the optimal temperature with respect to the pump power for balancing output powers of simultaneous emission is thoroughly explored. At the optimal temperature of 138 K, the total output power of the simultaneous emission can reach 3.1 W at an incident pump power of 7.9 W, corresponding to the optical to optical slope efficiency up to 43%.

A singly-resonant intracavity optical parametric oscillator (OPO), pumped by a passively Q-switched Nd:YAG laser, is systematically investigated by means of a series of the output mirrors with various reflectivities for the fundamental wavelength at 1064 nm. Experimental results reveal that the output mirror with partial reflectivity instead of high reflection at 1064 nm not only is practicable to avoid the optical coatings damaged, but also enhances the dual-wavelength output efficiency for the OPO signal and fundamental laser waves. The overall optical-to-optical conversion efficiency is enhanced from 6.4% to 8.2% for the reflectivity decreasing from 99.8% to 90%.

We exploit an ultra-low-magnification unstable resonator to develop a high-pulse-energy side-pumped passively Q-switched Nd:YLF/Cr4+:YAG laser with improving beam quality. A wedged laser crystal is employed in the cavity to control the emissions at 1047 nm and 1053 nm independently through the cavity alignment. The pulse energies at 1047 nm and 1053 nm are found to be 19 mJ and 23 mJ, respectively. The peak powers for both wavelengths are higher than 2 MW. Furthermore, the developed Nd:YLF lasers are employed to pump a monolithic optical parametric oscillator for confirming the applicability in nonlinear wavelength conversions.

A comparison between the fluorescence spectra of the Nd-doped vanadate crystals (Nd:YVO4, Nd:GdVO4, Nd:LuVO4) for the 4F3/2 → 4I11/2 transition is studied. We numerically analyze the condition of gain-to-loss balance via an uncoated intracavity etalon to achieve the dual-wavelength operation. We further experimentally demonstrate the orthogonally polarized dual-wavelength laser with a single Nd:LuVO4 crystal. The simultaneous dual-wavelength Nd:LuVO4 laser at 1085.7 nm in σ polarization and 1088.5 nm in π polarization is realized. At an incident pump power of 12 W, the average output power obtained at 1085.7 nm and 1088.5 nm is 0.4 W and 1.7 W, respectively.

A high-power efficient monolithic Nd:YAG 946-nm laser is demonstrated at the cryogenic temperature. By exploring the absorption and the fluorescence spectra of the Nd:YAG crystal, it reveals the fact that the absorption bandwidth at 808 nm is narrowing and the fluorescence intensity at 1061 nm is significant enhanced when the temperature is decreased. The temperature dependence of the lasing threshold at 946 nm is found to display a minimum value near a temperature of 170 K. At an incident pump power of 34.5 W, the local heating leads the optimum temperature to be approximately 120 K and the maximum output power can reach 24.4 W with the conversion efficiency of 71% as well as the slope efficiency up to 75%.

An energy adjustable passively Q-switched laser is demonstrated with a composite Nd:YAG/Cr⁴⁺:YAG crystal by applying a wedged interface inside the crystal. The theoretical model of the monolithic laser resonator is explored to show the energy adjustable feature with different initial transmissions of the saturable absorber at the horizontal axis. By adjusting the pump beam location across the Nd:YAG crystal, the output pulse energy can be flexibly changed from 10.9 μJ to 17.6 μJ while maintaining the same output efficiency. The polarization state of the laser output is found to be along with the polarization of the C-mount pump diode. Finally, the behavior of the multi-transverse-mode oscillation is also discussed for eliminating the instability of the pulse train.

We develop a theoretical model for designing a compact efficient multi-wavelength laser with dual gain media in a shared resonator. The developed model can be used to analyze the optimal output reflectivity for each wavelength to achieve maximum output power for multi-wavelength emission. We further demonstrate a dual-wavelength laser at 946 nm and 1064 nm with Nd:YAG and Nd:YVO4 crystals to confirm the numerical analysis. Under optimum conditions and at incident pump power of 17 W, output power at 946 nm and 1064 nm was up to 2.51 W and 2.81 W, respectively.

We employ a convex–concave resonator to develop a high-pulse-energy diode-side-pumped passively Q-switched Nd:YAG laser with high extraction efficiency. At a diode pump energy of 227 mJ, the output laser pulse reaches 30 mJ with a pulse width of 6 ns at a repetition rate of 20 Hz. The optical-to-optical conversion efficiency is up to 13.2%. Based on the developed Nd:YAG laser oscillator, we further employ a monolithic KTP crystal to perform the optical parametric oscillator (OPO). With the 1064 nm input energy of 30 mJ, the OPO energy at 1573 nm is found to be 13.3 mJ, corresponding to an OPO conversion efficiency as high as 44.3%.

We experimentally explore the fluorescence spectra of the Nd:YAG (YAG: yttrium aluminum garnet) crystal at cryogenic temperatures to confirm the feasibility of dual-wavelength operation at 1061 and 1064?nm. Furthermore, a cryogenically cooled Nd:YAG crystal with coating to form a monolithic cavity is employed to investigate the performance of the dual-wavelength operation. At an incident pump power of 20?W, the output powers for each wavelength can simultaneously reach 6.0?W at the optimally balanced temperature of 152?K. The optimal temperature for balancing the output powers of the two wavelengths is experimentally determined as a function of the incident pump power intensity.

We originally employ a compact combination of a Nd:YAG crystal and a Nd:YVO4 crystal to develop an efficient dual-wavelength laser operating at 946 and 1064 nm. We exploit a short Nd:YAG crystal to generate 946 nm laser by reducing the reabsorption loss and a follow-up Nd:YVO4 crystal to generate a 1064 nm laser by absorbing the residual pump light. The output power ratio between the 946 and 1064 nm emissions can be flexibly adjusted from 0.3 to 0.9 by varying the separation between the two output couplers. At an incident pump power of 17 W, the total output power is generally higher than 5.2 W, with an overall optical-to-optical efficiency greater than 30%.